You can easily reject an incoming call with a text message. Simply drag the small tab displayed below the call screen, choose a message and tap on Send to cancel the incoming call. You can have up to six different call rejection messages. To create a custom one: Go to Settings > Device > Call > Set Call Rejection Messages and tap on the + button displayed next to Create new message.
Create a call reject list
You can create a call reject list to block unknown numbers or unwanted contacts. Calls made from numbers added to the reject list are automatically forwarded to your voice mail. Open the Contacts app and then tap on the Menu button > Settings. Go to Call > Call rejection > Auto reject list. Tick the Unknown number checkbox to automatically block calls from unknown numbers. Tap on Create to create your call reject list.
Add a number to the reject list
Tap on the Contacts icon and select the number from your contact list or call log. Alternatively you can use the Enter number field to add a specific phone number.
Automatically block numbers matching specific criteria
You can also create a filter to block calls from phone numbers that match a certain criteria (specific region code, prefix...). Tap on Match Criteria and select a filter: Exactly the same as, Starts with, Ends with or Includes.
Tap on Save to apply your new settings.
Remove a contact from the reject list
If you changed your mind and want to allow calls from a blocked contact, then simply edit its corresponding entry in the reject list. Open the reject list and clear the checkbox appearing next to the contact your want to unblock to allow call and messages from the latter. If you want to permanently remove the selected contact from the reject list, then simply tap on the Trash icon displayed at the top right corner of your screen.